Air-fuel ratio control device for internal combustion engine

Abstract

The present invention relates to an air-fuel ratio control device for an internal combustion engine, and makes it possible to maintain high purification performance by suppressing a decrease in the oxygen occlusion capability of a catalyst. When an O2 sensor output oxs is greater than a reference value oxsref, which corresponds to a stoichiometric air-fuel ratio, and smaller than an upper threshold value oxsrefR, a sub-FB reflection coefficient is fixed at a predetermined value vdox2 for providing a lean air-fuel ratio. When, on the other hand, the O2 sensor output oxs is smaller than the reference value oxsref and greater than a lower threshold value oxsrefL, the sub-FB reflection coefficient is fixed at a predetermined value vdox2 for providing a rich air-fuel ratio. The sub-FB reflection coefficient reflects the O2 sensor output oxs in the calculation of a fuel injection amount and increases or decreases to have a consequence on the air-fuel ratio of an exhaust gas.

Description

TECHNICAL FIELD[0001]The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to an air-fuel ratio control device for an internal combustion engine having an exhaust path in which a catalyst capable of occluding oxygen is installed.BACKGROUND ART[0002]Catalysts used for exhaust gas purification in an internal combustion engine have an oxygen occlusion capability for occluding oxygen in them. When the air-fuel ratio of an exhaust gas flowing into a catalyst is lean, the catalyst occludes oxygen in the gas. When, on the other hand, the air-fuel ratio of the exhaust gas flowing into the catalyst is rich, the catalyst releases the occluded oxygen into the gas. Therefore, when the exhaust gas has a lean air-fuel ratio and contains a relatively large amount of NOx as compared with HC and CO, the catalyst occludes oxygen to reduce NOx. When, on the other hand, the exhaust gas has a rich air-fuel ratio and contains a relative...

AI Technical Summary

Problems solved by technology

However, if the air-fuel ratio of the exhaust gas flowing into the catalyst continues to deviate toward the lean side, the oxygen occluded by the catalyst reaches saturation before long so that NOx cannot be purified.

If, in contrast, the air-fuel ratio continues to deviate toward the rich side, the oxygen occluded by the catalyst is depleted before long so that HC and CO cannot be purified.

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